Laptop turns on and off and doesn't turn on

Hello,

i was on firefox yesterday and the page that was open turned grey and the computer froze up and then shut it down and now it will not restart. It starts shows the windows xp and then black screen and turns off again and continues to turn on and off untill I manually turn it off. It doesn't work when in safe mode etc either. does the same thing. I was working with Mcafee a week ago to remove malware/virus etc. but was having problems with them completing the clean up.